1. Field of the Invention
The present invention generally relates to a mobile communications system providing mobile communication services or personal communication services by delivering a paging signal through an ATM (asynchronous transfer mode) transmission system, and in particular to a method for checking an ATM point-to-multipoint connection of the ATM transmission system.
2. Description of the Related Art
In a mobile communications system having a service area consisting of a plurality of radio zones, a selective calling signal or a paging signal is transmitted to determine whether a destination mobile terminal is located within the service area. As the number of subscribers increases, a very large number of paging signals are transmitted in the mobile communications system, resulting in reduced performance capacity of mobile switches and base stations. In the field of CDMA (code-division multiple access) mobile communications systems using ATM transmission system, multicast techniques of paging signals have been developed by making use of ATM point-to-multipoint function; copy-trunk method and multicast-connection method.
According to the copy-trunk method, as shown in FIG. 1, a point-to-point connection has been set up between ATM transmission system 11 and each of N base stations B1-BN, where N is an integer. When an incoming call occurs, a paging signal transmitter 12 of mobile switch equipment 10 transmits a paging signal to a copy trunk section 13 of the ATM transmission system 11. The copy trunk section 13 converts the paging signal to an ATM paging cell CELLPG and makes N copies of the ATM paging cell CELLS corresponding to the base stations B1-BN, respectively. The respective ATM paging cell CELLPG are sent to the base stations B1-BN through the setup point-to-point connections.
Since the point-to-point connections have been set up, an OAM (operation, administration and maintenance) cell can be used to test the ATM lines for continuity. More specifically, the test for ATM lines can be carried out by sending an OAM cell through each of the ATM point-to-point connections and then checking whether each OAM cell is sent back by the corresponding base up station.
On the other hand, according to the multicast-connection method, as shown in FIG. 2, the ATM transmission system 11 has had a point-to-multipoint connection set up between a paging transmitter 14 of the mobile switch equipment 10 and the base stations B1-BN . When an incoming call occurs, the paging transmitter 14 converts the paging signal to an ATM paging cell CELLPG and transmits it to the base stations B1-BN through the point-to-multipoint connection set up in the ATM transmission system 11.
The above copy-trunk method and multicast-connection method, however, have disadvantages as described hereinafter. In the copy-trunk method, it is necessary to set up an ATM point-to-point connection for each subscriber paging line, resulting in increased amount and complexity of equipment. In the case of a communications system having relatively small radio zones such as micro-cells or pico-cells, setting up ATM connections become complicated because a large number of base stations have to be arranged to meet various calling needs. Further, the point-to-point connection provides not only a connection from the paging signal transmitter 12 to the base stations but also the opposite connection. Since the paging operation can be performed using only the former, the equipment for the latter becomes redundant.
In the multicast-connection method, the one-to-multipoint connection is set up in the ATM transmission system 11 to deliver the ATM paging cells to the base stations. However, the opposite multipoint-to-point connection cannot be set up. Therefore, it is impossible to test the ATM lines for continuity using an OAM cell.
An object of the present invention is to provide a check method which can check AM point-to-multipoint connection between a paging transmitting side and a plurality of paging receiving side with reliability.
Another object of the present invention is to provide a check method which can check ATM point-to-multipoint connection between a paging transmitter and a plurality of base stations of a mobile communications system with reduced amount and complexity of hardware.
The present invention is a method for checking a point-to-multipoint connection set up in an ATM transmission system between a paging sender and a plurality of paging receivers in a mobile communications system.
According to a first aspect of the present invention, the paging sender sets up the point-to-multipoint connection in the ATM transmission system and transmits a check cell to the paging receivers through the point-to-multipoint connection at intervals of a first predetermined time period. Each of the paging receivers determines whether the check cell is received within a second predetermined time period longer than the first predetermined time period. When the check cell has not been received for the second predetermined time period, a connection resetting request Is transmitted to the paging sender to reset the point-to-multipoint connection.
According to a second aspect of the present invention, the paging sender sets up the point-to-multipoint connection in the ATM transmission system and transmits a paging cell to the paging receivers through the point-to-multipoint connection when an incoming call occurs. Each of the paging receivers determines whether a paging cell is received within a first predetermined time period and transmits a check request to the paging sender when a paging cell has not been received for the first predetermined time period. The paging sender transmits a check cell to the paging receivers through the point-to-multipoint connection in response to the check request received from at least one of the paging receivers. The paging receiver determines whether the check cell is received within a second predetermined time period after the check request has been transmitted, and then transmits a connection resetting request to the paging sender to reset the point-to-multipoint connection when the check cell has not been received for the second predetermined time period.
According to a third aspect of the present invention, the paging sender sets up the point-to-multipoint connection in the ATM transmission system and transmits a paging cell to the paging receivers through the point-to-multipoint connection when an incoming call occurs. Each of the paging receivers transmits a paging response to the paging sender when a paging cell is received. The paging sender determines whether there is a paging receiver from which the paging response has not been received for a predetermined time period, and resets the point-to-multipoint connection when there is at least one paging receiver from which the paging response has not been received for the predetermined time period.
According to a fourth aspect of the present invention, the paging sender sets up the point-to-multipoint connection in the ATM transmission system, and transmits a check cell to the paging receivers through the point-to-multipoint connection at intervals of a first predetermined time period. Each of the paging receivers transmits a paging response to the paging sender when a paging cell is received. The paging sender determines whether there is a paging receiver from which the paging response has not been received for a second predetermined time period, and resets the point-to-multipoint connection when there is at least one paging receiver from which the paging response has not been received for the second predetermined time period.